Method of and apparatus for circulating liquid metals in fused salt electrolysis

ABSTRACT

A method of and an apparatus for circulating a liquid metal in fused salt electrolysis comprising passing the fused alloy of the cathode liquid metal and the electrolytically liberated metal both coming out of the cell and the liquid metal for controlling the temperature of the cell through a lift pipe by making a mixture of an inert gas and the liquid metals by the jetting force of the gas, said mixture being small in specific gravity, lifting said liquid metals into a head tank positioned at a level high enough for recirculating the liquid metals into the electrolytic cell by gravity, separating the liquid metals from the inert gas in said head tank, recirculating the liquid metal necessary for electrolysis into the cell, condensing and separating the electrolytically liberated metal contained in the inert gas from the gas, and returning the inert gas into the lift pipe for further use by circulation.

nited States Patent Sakai et al.

[ 5] Feb. 15, 1972 [54] METHOD OF AND APPARATUS FOR CIRCULATING LIQUID METALS IN FUSED SALT ELECTROLYSIS [72] Inventors: I-Iidetami Sakai, Room No. 501, Building No. 182, 22, 3-chome, Takanedai- Danchi, Takanedai-cho, Funabashi-shi; Muneyoshi Arita, 68-556, Joza, Sakurashi, both of Japan [22] Filed: Mar. 10, 1970 [21] Appl.No.: 18,103

[52] US. Cl. ..204/247, 204/220, 204/239 1,597,231 8/1926 Haynes ..204/247 X 3,167,492 1/1965 Szechtman ..204/68 3,546,021 12/1970 Craig ..204/242X Primary Examiner-John H. Mack Assistant Examiner-D. R. Valentine Attorney-Holman & Stern [57] ABSTRACT A method of and an apparatus for circulating a liquid metal in fused salt electrolysis comprising passing the fused alloy of the cathode liquid metal and the electrolytically liberated metal both coming out of the cell and the liquid metal for controlling the temperature of the cell through a lift pipe by making a mixture of an inert gas and the liquid metals by the jetting force of the gas, said mixture being small in specific gravity, lifting said liquid metals into a head tank positioned at a level high enough for recirculating the liquid metals into the electrolytic cell by gravity, separating the liquid metals from the inert gas in said head tank, recirculating the liquid metal necessary for electrolysis into the cell, condensing and separating the electrolytically liberated metal contained in the inert gas from the gas, and returning the inert gas into the lift pipe for further use by circulation.

2 Claims, 2 Drawing Figures METHOD OF AND APPARATUS FOR CIRCULATING LIQUID METALS IN FUSED SALT ELECTROLYSIS BACKGROUND OF THE INVENTION In the method of producing an alkali metal and an alkaline earth metal with a conventional fused salt electrolytic equipment the fused alloy of the cathode liquid metal and the electrolytically liberated metal is distilled and separated and the liquid metal is recirculated into the electrolytic cell to be used as the cathode. In this circulating line a mechanically circulating pump is employed. In some case, the electrolytic cell is provided with a flow passage at a side or at the bottom thereof through which a liquid metal is passed as the medium for heat to control the temperature of the cell so that the conditions of electrolysis can be stabilized. In the circulating line, too, a mechanically circulating pump is employed.

The electrolysis of fused salt is operated at a considerably high temperature. The alloy of the cathode liquid metal and the electrolytically liberated metal both coming out of the cell and the metal for controlling the temperature of the cell must be circulated to each process of the equipment at high temperatures. However, there are various troubles about the circulation of the liquid metals at high temperatures. For instance, there are the problems of corrosion of the materials of the equipment with the liquid metal, the alloy of the liquid metal and the liberated metal, and the temperature-controlling circulating liquid metal, the heat resistance of the equipment itself, and the heat insulation of the high temperature equipment. Also the mechanically circulating pump such as an electromagnetic pump or a centrifugal pump is liable to get troubles at its shaft seal and other parts. Especially, the complexity of the construction of the equipment increases the possibility of troubles and it is often difficult to secure the safety of operation. All these undesirable factors cause the service life of the equipment to be shortened and the cost of fused salt electrolysis to be raised.

SUMMARY OF THE INVENTION The present invention mainly comprises circulating the liquid metal into fused salt electrolytic cell in which a fused metal is used as the cathode by the jetting force of an inert gas instead of using a mechanically circulating pump in the liquid metal-circulating line. This method of circulating the liquid metal simplifies the construction of the equipment. facilitates the selection of heat-resistant materials and heat-insulating materials, and assures the safety of operation, thus resulting in many advantageous effects.

More specifically, this invention provides a method of and an apparatus for circulating the liquid metal into said fused salt electrolytic cell comprising passing the fused alloy of the cathode liquid metal and the electrolytically liberated metal produced in the gap between the cathode and anode through the lift pipe together with the inert gas by the jetting force of the gas, making a mixture of the alloy and the inert gas in the lift pipe by the jetting force of the gas, said mixture being small in specific gravity, transporting the electrolytically liberated metal vapor alone into the inert gas in said lift pipe lifting said mixture into the head tank, separating the cathode liquid metal from the inert gas containing the electrolytically liberated metal in the tank, condensing and separating the electrolytically liberated metal from the inert gas, cooling, compressing and circulating the inert gas for repeated use, and returning the liquid metal remaining on the bottom of said head tank to the electrolytic cell for reuse.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows diagrammatically the circulating line of a fused salt electrolytic equipment suitable for carrying out the method of the present invention.

FIG. 2 shows diagrammatically the circulation device for the alloy of fused metals and the temperature-controlling liquid metal in the electrolytic cell of the fused salt electrolytic equipment.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, the electrolytic cell 1 is heated by the heater 22. The receiver 2 for receiving the alloy produced by electrolysis is also heated by the heater 23. 3 is the lift pipe standing upright in said receiver 2, 4 the head tank, 5 the condenser, 6 the heat exchanger also serving as gas cooler, and 7 the gas compressor, respectively. The alloy 10 of the cathode liquid metal 8 and the electrolytically liberated metal 20 produced by electrolysis in the gap between said cathode liquid metal 8 and the anode 9 made of graphite for instance in the electrolytic cell 1 enters the receiver 2 placed at a level lower than that of the cathode liquid metal 8 through the pipe 11. In the receiver 2 is standing the lift pipe 3. The lift pipe 3 has a length equal to the sum of the height of that part of the receiver 2 which is immersed in the alloy 10 contained therein and the length of the part lifting the alloy 10. Said length of the lift pipe 10 should be such that when the lift pipe 3 is planted upright in the receiver 2 the upper end of said lift pipe 3 will come to a level at least higher than that of the cathode liquid metal 8 in the electrolytic cell 1. In other words, since the lift pipe needs to have a head large enough to return the alloy 10 to the electrolytic cell 1, it should have a length equal to the sum of a length a little greater than the height of the level of said cathode liquid metal 8 and an optional length added. lmmediately below the lift pipe 3 is provided the nozzle 13 of the inner gas conduit 12, and when a suitable volume of the inert gas 14 is jetted out at said nozzle 13 into the liquid alloy 10 the mixture 15 of the alloy 10 and the inert gas 14 is produced in the lift pipe 3. This mixture 15 is smaller than the alloy 10 in specific gravity. The buoyancy created by the difference in specific gravity and the jetting force of said inert gas 14 combine to serve as a driving force to lift the mixture 15 through the lift pipe 3 into the head tank 4 provided at the upper end of said lift pipe 3. At the same time the electrolytically liberated metal 20 alone has its vapor transported into the inert gas 14 by the effect of the pressure at its temperature. The liquid metal 8 is separated from the inert gas 14 containing the liberated metal 20 in the head tank 4. The inert gas 14 containing the liberated metal 20 is introduced into the condenser 5 through the pipe 17 connected to the upper part of the head tank 4, and the liberated metal 20 is condensed and separated from the inert gas 14 in said condenser 5 and then taken out at the discharge pipe 25. On the other hand, the separated inert gas 14 is transported into the heat exchanger/gas cooler 6 through the pipe 18 and cooled there to a suitable temperature. Then it is conveyed further to the compressor 7 through the pipe 19 to be made into compressed inert gas 14 and finally blown into said lift pipe 3 through the pipe 12 for recirculation. The liquid metal 8 left behind in the head tank 4 flows down by gravity into the electrolytic cell 1 as the cathode liquid metal 8 for recirculation through the pipe 24 connected to a side of the head tank 4 at a level lower than the upper end of the lift pipe 3.

In the case where the vapor pressure of the alloy 10 of the cathode liquid metal 8 and the electrolytically liberated metal 20 is low, the separation of the liberated metal 20 from the inert gas 14 containing the liquid metal 8 if facilitated by heating said alloy 10 by the heater 23 provided under the receiver 2. If the inert gas 14 coming out of the compressor 7 is passed into the gas cooler 6 for heat exchange and blown into the nozzle 13 in a warmed state, the heat may be economized. In the condenser 5 the inert gas 14.is cooled to the degree that the liberated metal 20 can be taken out at a temperature a little higher than the melting point of said liberated metal 20. As the liberated metal 20 thus condensed and separated generally contains slight quantities of the cathode liquid metal 8, it is advisable to rectify the liberated metal 20 by a rectifier (not shown) to obtain high purity liberated metal 20. It is possible to produce compounds of the liberated metal 20 by adding other metals directly to the inert gas 14 containing the liberated metal vapor 20.

This equipment can not only lift the alloy 10 in the receiver 2 to required height through the lift pipe 3 by the jetting force of the inert gas 14 but also make a mixture 15 of the alloy 10 and the inert gas 14 by said jetting force and transport only the liberated metal vapor into the inert gas 14 to separate the liberated metal 20 from the cathode liquid metal 8 without resorting to distillation.

The cathode liquid metal used in the present invention may be lead, tin, bismuth, or alloy of two or more of these, the fused salt may be a halide of any of alkali metals or alkaline earth metals or a combination of these, and the inert gas may be argon or nitrogen.

Now an embodiment of this invention will be described in detail by referring to FIG. 1. In the fused sodium chloride electrolytic equipment employing fused lead as cathode, the horizontal electrolytic cell 1 has a metal bottom plate and corrosion resisting brick-lined sideplates. Fused lead and fused sodium chloride are introduced into this electrolytic cell 1, and said sodium chloride is electrolyzed at a temperature of 850 C. to produce a lead alloy 10 containing about 10 percent by weight of sodium. Said alloy is introduced into the receiver 2 150 mm. in inside diameter and 1,500 mm. high, in which stands said lift pipe mm. in inside diameter and 3,000 mm. long. Said head tank 800 mm. by 800 mm. square and 1,500 mm. high is installed with its bottom at a level 300 mm. below the top of said lift pipe 3. The lower end 21 of said lift pipe 3 is open in the shape of a funnel, 100 mm. below which is arranged the pipe 12 having said nozzle 12 mm. in inside diameter for blowing out nitrogen gas. When the nitrogen gas is jetted out at this nozzle at a pressure of about 1.4 kg./cm. G and at a rate of 1.0 liter/second, the fused lead is lifted into the head tank 4 at a rate of 0.1 l liter/second. By cooling the nitrogen gas containing the sodium vapor to 350 C. in the condenser 5, we obtained 1.17 kg./hour of sodium. The nitrogen gas was cooled to 50 C. in the gas cooler 6, compressed at 2 kg./cm G in the oil-free compressor 7, and recirculated. The fused lead in the head tank 4 was returned to the electrolytic cell 1 for recirculation. In case the capacity of the lift pipe to lift the fused lead is large for the electrolyzing capacity of the cell, part of the fused lead can be conveniently circulated between the receiver 2 and the tank 4.

FIG. 2 shows a flowsheet of the said equipment installed together with a device for circulating a liquid metal for controlling the temperature of the electrolytic cell. The cathode liquid metal, fused salt and inert gas used in this embodiment are the same as those used for the previous one. is the electrolytic cell provided at its bottom with the flow passage 31 for passing the temperature-controlling liquid metal and with the heating section 74. 32 is the receiver for receiving the liquid metal remaining in the distiller, said receiver 32 having the heating section 75. 33 is the receiver for receiving the liquid metal for controlling the temperature of said electrolytic cell 30, said receiver 33 having the heating section 76. 34 and 35 are the lift pipes each planted in the receivers 32 and 33, 36 and 37 the head tanks, 38, 39, 40 and 41 the inert gas coolers, 42 the gas supplying compressor, and 43 the heat exchanger for the liquid metal, respectively. The circulating line for the alloy 46 of the cathode liquid metal 44 and the electrolytically liberated metal produced by electrolysis in the gap between cathode liquid metal 44 and the anode 45 in the electrolytic cell 30 is the same as that for the previous embodiment. Namely, the alloy 46 is introduced into the receiver 32 through the conduit 47. The receiver 32 is so installed that the lever of the liquid metal 48 contained in said receiver 32 will come to a level lower than that of the liquid metal remaining on the bottom of the cell 30. In the receiver 32 is planted the lift pipe 34, the upper end of which should come to an optional level higher than that of the cathode liquid metal 44. The orifice 50 at the lower end of the immersed lift pipe 34 is fronted from below by the nozzle 51 of the conduit 72 coming from the compressor 42. The inert gas 52 jetted out flows into said lift pipe 34 through the orifice 51 and makes a mixture 53 of the liquid metal 48 and the inert gas 52 having small specific gravity. Said mixture 53 rises in the lift pipe 34 by the jetting force of the inert gas 52 and is lifted into the head tank 36 provided above, where the liquid metal 48 and the inert gas 52 are separated from each other by the difference of specific gravity. The liquid metal 48 thus separated in the head tank 36 flows down into the electrolytic cell 30 by gravity through the connecting pipe 55 and is circulated again as the cathode liquid metal 44 to make the alloy with the electrolytically liberated metal.

As for the circulation of temperature-controlling liquid metal 56, the temperature-controlling liquid metal 56 coming from the bottom plate 57 of the cell 30 or through the outlet 58 of the tunnel-shaped flow passage 31 provided in said bottom plate 57 is introduced into the receiver 33 installed at a level lower than that of said outlet 58. In the receiver 33 is planted the lift pipe 35 as in the case of the above-mentioned receiver 32. The inert gas 52 supplied through the conduit 73 of said compressor 42 is blown at the nozzle 61 into the lift pipe 35 through the orifice 60 at the lower end thereof. The mixture 62 of the liquid metal 56 and the inert gas 52 is lifted into the head tank 3 provided above the lift pipe 35 through said lift pipe 35. The liquid metal 56 separated from the inert gas 52 in said head tank 36 flows down through the pipe 64 connected to the outlet 63 of the head tank 36 and enters the heat exchanger 43. In order that the electrolytic cell 30 containing said liquid metal 44 can be kept at a suitable temperature, said liquid metal 56 heated or cooled in said heat exchanger 43 is discharged from the heat exchanger 43 and flows by gravity into the inlet 70 of the flow passage 31 of the cell 30 and then, after controlling the temperature of the electrolytic cell 30 to a level suitable for electrolysis of the fused salt, returns to the receiver 33 through the pipe 59 for recirculation.

The inert gas 52 used as driving force in the circulating lines of the cathode liquid metal 44 and of the temperature-controlling liquid metal 56 is separated in the head tanks 36 and 37 respectively. The metal vapor contained in small quantities in the inert gas 52 is collected and separated in the coolers 38 and 39 installed above the head tanks 36 and 37 respectively to prevent the metal vapor from solidifying and choking the circulating lines. After being made free from the metal vapor the inert gas 52 is further introduced in the coolers 40 and 41 through the pipes 65 and 66 to be cooled to a temperature substantially suitable for giving not troubles to the compressor 42. Then the inert gas 52 is returned to the compressor 42 through the pipes 67 and 68 compressed to a specified pressure high enough to work as the driving force for circulating. During all this time the operation is carried out with the pressure kept slightly higher than the atmospheric pressure to prevent the entry of air into the inert gas piping. The inert gas 52 at said specified pressure is blown into the lift pipes 34 and 35 through the nozzles 51 and 61 provided below them to circulate the cathode liquid metal and the temperature-controlling liquid metal.

ln the embodiment shown in FIG. 2 the numerical values are the same as those for the previous one and liquid lead is circulated in the temperature control circulating line. It was possible to stabilize the operational conditions of the electrolytic cell by keeping the temperature of liquid lead a 900 C. at its inlet and at 850 C. at its outlet by means of the heat exchanger 43. The fused salt, therefore, was electrolyzed in a highly stabilized state.

Since both equipment shown in FIG. 1 and FIG. 2 do not need the use of mechanically circulating pumps in the liquid metal-circulating lines, no sever conditions of materials or complicated constructions are required of the whole equipment, the design of the equipment is simplified with regard to influences of thermal stress, and 'no special kind of insulating means are necessary for the piping. For these reasons, relatively low-priced materials may be used, the repair and replacement are easy, the safety of operation is high, and the service life is long.

What we claim is:

1. An apparatus for circulating a liquid metal in fused salt electrolysis using a liquid metal as the cathode comprising a receiver for receiving the fused alloy of electrolytically liberated metal and cathode liquid metal produced in the gap between the cathode and anode, said receiver being installed at a level lower than that of said cathode liquid metal; a lift pipe standing in said receiver, said lift pipe having such a length that its upper end will come to a level higher than that of the liquid metal in the electrolytic cell, a head tank connecting to said lift pipe, said head tank being installed above said pipe with its bottom at a level a little lower than the upper end of said lift pipe and yet higher than that of the cathode liquid metal in the electrolytic cell; a nozzle for jetting out the inert gas, said nozzle being positioned at a place facing the lower orifice of said lift pipe and connecting to a compressor for supplying the inert gas through a conduit so that the abovementioned alloy may be jetted and lifted into said head tank through said lift pipe together with the inert gas as a mixture; a conduit connecting a side or the bottom of the head tank to the electrolytic cell for flowing down the cathode liquid metal; a condenser for condensing the vapor of electrolytically liberated metal contained in the inert gas, said condenser being connected to the extended portion of the conduit above the head tank for discharging the inert gas containing the electrolytically liberated metal vapor; and a cooler for the inert gas, connected both to said extended portion of the conduitand to said compressor for circulating the inert gas.

2. An apparatus for circulating a liquid metal defined in claim 1, wherein the apparatus comprisesa flow passage at the bottom of the electrolytic cell for flowing a liquid metal for controlling the temperature of the cell; a receiver for receiving said temperature-controlling liquid metal, said receiver being installed at a level lower than said flow passage; a lift pipe standing upright in said receiver a head tank connecting to said lift pipe, said head tank being installed above said pipe with its bottom at level a little lower than the upper end of said lift pipe and yet higher than said flow passage; a nozzle for jetting out the inert gas, said nozzle being positioned immediately below said lift pipe; a conduit connecting said nozzle to the compressor so that the inert gas jetted out of said nozzle may be lifted into the head tank through said lift pipe together with the liquid metal as a mixture; a conduit connecting said head tank to the electrolytic cell for flowing down the temperature-controlling liquid metal; and a conduit for discharging the inert gas, said conduit being positioned above the head tank and connecting to said compressor. 

2. An apparatus for circulating a liquid metal defined in claim 1, wherein the apparatus comprises a flow passage at the bottom of the electrolytic cell for flowing a liquid metal for controlling the temperature of the cell; a receiver for receiving said temperature-controlling liquid metal, said receiver being installed at a level lower than said flow passage; a lift pipe standing upright in said receiver a head tank connecting to said lift pipe, said head tank being installed above said pipe with its bottom at level a little lower than the upper end of said lift pipe and yet higher than said flow passage; a nozzle for jetting out the inert gas, said nozzle being positioned immediately below said lift pipe; a conduit connecting said nozzle to the compressor so that the inert gas jetted out of said nozzle may be lifted into the head tank through said lift pipe together with the liquid metal as a mixture; a conduit connecting said head tank to the electrolytic cell for flowing down the temperature-controlling liquid metal; and a conduit for discharging the inert gas, said conduit being positioned above the head tank and connecting to said compressor. 